1. Field of the Invention
The present invention relates to a novel catalyst for the treatment of exhaust gases from internal combustion engines, and to a process for the production thereof.
This invention especially relates to a catalyst support of the monolithic type, the inert and rigid substrate of which is coated with a layer of a porous material, as well as to the catalyst produced by impregnation of such support with catalytically active elements.
2. Description of the Prior Art
In the catalytic treatment of vehicular exhaust gases emanating from internal combustion engines, the catalytic converters are typically charged with monolithic catalysts. These catalysts comprise a rigid and inert support upon which a layer of a porous material, such as for example alumina, is deposited, said layer in turn being impregnated with a catalytically active phase. A process for the preparation of such a catalyst and, in particular, of a monolithic support coated with a porous material is described in EP No. 73,703. This process makes it possible to deposit a layer of a porous material, e.g., alumina, onto a monolithic metallic or refractory ceramic substrate.
This process also provides for the partial replacement of alumina with other metallic oxides.
It is also known to this art that the rare earth oxides and, in particular, cerium oxide, when added to the alumina constituting the porous coating, improve the thermal stability and efficiency of the catalyst. These effects are of significant importance in the treatment of the exhaust gases from internal combustion engines, during which the catalysts are heated to elevated temperatures.
Monolithic catalyst supports, the porous coating of which is a metallic aluminate having a spinel structure, such as a magnesium aluminate, have also been proposed to this art. However, these coatings, which have adequate thermal stability, display the major disadvantage of possessing a very low specific surface. Thus, only a small amount of catalytically active elements can be deposited onto the coated supports, and this appreciably reduces the life of the catalyst.
The catalysts heretofore known to this art have the disadvantage of being highly sensitive to the presence of sulfur or sulfur compounds in the exhaust gas. In fact, sulfur serves as a poison and effectively reduces the useful life of such catalysts.